DIETARY-FAT TYPE AND LEVEL INFLUENCE ADIPOSITY DEVELOPMENT IN OBESE BUT NOT LEAN ZUCKER RATS

The development of obesity is influenced by a variety of factors inclu ding genetics and dietary:at type and level. To examine the interactio n between these factors, male lean and obese Zucker rats (5 weeks Init ial age) were fed either a low-fat (15% calories) or one of two high-f at diets (65% calories; predominant fat source of either soybean oil o r palm olein) for 8 weeks. Body weight, food intake, indirect calorime try, and body composition determinations were performed, As expected, food Intake, body weight, feed efficiency, oxygen consumption, heat pr oduction and carcass lipid were all significantly higher in abase comp ared to lean rats. Dietary fat level and/or type influenced body weigh t gain, oxygen consumption, heat production, energy balance, and carca ss weight and lipid content in the obese but not in the lean Zucker ra ts. Oxygen consumption and carcass weight were increased approximately 25% and 10% respectively in obese rats fed either of the two high-fat diets as compared to those fed the low-fat diet. The type of fat fed in the high-fat diets also influenced body weight gain, hear productio n, energy balance, and carcass lipid content of the obese rats. Body w eight gain and carcass lipid content were increased (16%-17%; P < 0.00 5) in obese rats fed the high-fat palm olein diet as compared to those fed the low-far diet. These parameters were not increased in obese ra ts fed the high-fat soybean oil diet, in contrast, indirect calorimetr y measurements indicated a moderate increase in heat production (Kcal/ effective body mass/day; 14.5%) and decrease in energy balance (44.8%) in the obese rats fed the high-fat soybean oil diet as compared to th ose fed the low-Pat diet. Energy expenditure and lipid accumulation we re negligibly influenced by dietary fat level or type in the lean Zuck er rats. The differential response of the lean and obese Zucker rats t o this short-term dietary manipulation demonstrate that genetic backgr ound can influence an individual's response to dietary fat type and le vel. The genetically obese Zucker rat appears to be a good model for f urther studies of high-fat diet-induced obesity.